The present disclosure relates to an azoquinone compound, to an electrophotographic photoconductor that contains the azoquinone compound in a photoconductive layer, and to an image forming apparatus that is provided with the electrophotographic photoconductor.
Recent years have witnessed the development of organic compounds having various functions, such as charge transport properties and photoconductivity, and studies are being conducted on the use of such compounds in various fields, for instance electronic materials. The object of such studies is, for instance, the use of organic compounds having charge transport properties, among such organic compounds, in the field of organic photoconductors, organic EL elements, dye-sensitized solar cells and the like.
Among the foregoing, for instance, organic photoconductors are photoconductors for electrophotography that are provided in electrophotographic-type image forming apparatuses. Examples of electrophotographic photoconductors that are provided in such electrophotographic-type image forming apparatuses include, besides organic photoconductors, also inorganic photoconductors that is provided with a photoconductive layer made up of an inorganic material such as selenium, amorphous silicon or the like. Organic photoconductors are provided with a photoconductive layer that contains, as a main component of a photoconductor material, an organic material such as a charge generating agent, a charge transport agent or the like, in a binding resin. Organic photoconductors are known to afford, as a result, a wider range of choice as regards the photoconductor material that makes up the photoconductive layer, and a greater degree of freedom in terms of structural design, as compared with inorganic photoconductors.
Electrophotographic photoconductors are further required to exhibit for instance excellent photosensitivity, in order to form high-quality images. To obtain such electrophotographic photoconductors having excellent photosensitivity, the charge transport agent contained in the photoconductive layer must satisfy various conditions.
Both multilayer-type organic photoconductors and single layer-type organic photoconductors are being developed. Ordinarily, the charge transport agent used in these organic photoconductors is a hole transport agent in multilayer-types, and a hole transport agent and an electron transport agent in single layer-types. Conditions that apply to the foregoing photoconductors stipulate, for instance, that the charge transport agent should have high charge transport ability, appropriate ionization potential in order to take up efficiently the charge generated by the charge generating agent, high solubility in an organic solvent, such as tetrahydrofuran or the like, being the solvent of a coating solution that is used to form the photoconductive layer, and compatibility with the binding resin contained in the photoconductive layer.
Specific conventional examples of the electron transport agent that is included in the photoconductive layer of such an electrophotographic photoconductor include, for instance, naphthoquinone derivatives of predetermined structure, specifically, the naphthoquinone derivative represented by formula (7) below.
The above naphthoquinone derivative is known to have excellent electron transport ability and comparatively good solubility in solvents and compatibility with binding resins. Electrophotographic photoconductors in which this naphthoquinone derivative is used as an electron transport agent are known to have comparatively high sensitivity.
Meanwhile, image forming apparatuses provided with an electrophotographic photoconductor are required to afford yet higher image quality in the images that are formed therewith. For the reasons above, the material that is included in the photoconductive layer of the organic photoconductor that is used as an electrophotographic photoconductor provided in the image forming apparatus has to be a material such that, by being incorporated into the photoconductive layer, an electrophotographic photoconductor is obtained that allows forming images of yet higher quality. Specifically, the electrophotographic photoconductor is required to have yet better photosensitivity. That is, the material included in the photoconductive layer of the organic photoconductor has to be a material such that, by being incorporated into the photoconductive layer, a photoconductive layer is obtained that has yet better photosensitivity. In a case where the material is incorporated, as an electron transport agent, into the photoconductive layer of the electrophotographic photoconductor, a material is required that yields a photoconductive layer of better photosensitivity than in the case where the above naphthoquinone derivative is incorporated into the photoconductive layer.
In the light of the above, it is an object of the present invention to provide an azoquinone compound which, when incorporated into the photoconductive layer of an electrophotographic photoconductor, affords an electrophotographic photoconductor of excellent photosensitivity. A further object of the present invention is to provide an electrophotographic photoconductor that contains the azoquinone compound in a photoconductive layer, and to provide an image forming apparatus that is provided with the electrophotographic photoconductor.